Evaluating minimal important differences for the FACT-melanoma quality of life questionnaire

Objectives: Minimal Important Differences (MIDs) establish benchmarks for interpreting mean differences in clinical trials involving quality of life outcomes and inform discussions of clinically meaningful change in patient status. The purpose of this study was to assess MIDs for the Functional Assessment of Cancer Therapy-Melanoma (FACT-M). Methods: A prospective validation study of the FACT-M was performed with 273 patients with stages I through IV melanoma. FACT-M, Karnofsky Performance Scales, and Eastern Cooperative Oncology Group Performance Status scores were obtained at baseline and 3 months following enrollment. Anchor- and distribution-based methods for assessing MIDs were compared, and pattern-mixture modeling was employed to derive multivariate adjusted estimates. Results: This study indicates that an approximate range for MIDs of the FACT-M subscales is between 5 to 9 points for the Trial Outcome Index, 4 to 6 points for the Melanoma Combined Subscale, 2 to 4 points for the Melanoma Subscale, and 1 to 2 points for the Melanoma Surgery Subscale. Each method produced similar but not identical ranges of MIDs. Conclusions: The properties of the anchor instrument employed to derive MIDs directly affect resulting MID ranges and point values. When MIDs are offered as supportive evidence of a clinically meaningful change, the anchor instrument used to derive clinically meaningful thresholds of change should be clearly stated along with information supporting the choice of anchor instrument as the most appropriate for the domain of interest.